1. Field of the Invention
This invention relates to a temperature control device for drying ovens for mirror protective paint.
2. Discussion of Background
In mirror manufacture, the initial glass sheet, after suitable polishing, is coated on one face, in the stated order, with a layer of silver, a layer of copper and a layer of paint the purpose of which is to protect the underlying layers from environmental attack. In modern plants, the said operations are carried out on moving glass sheets with the plants operating continuously. After applying the various layers, the sheets, now converted into mirrors, pass through a continuous oven for drying the paint. These ovens have zones of different presettable temperatures so that an optimum temperature profile is obtained along the oven. The temperature of the various oven sections is set on conventional temperature control apparatus and is measured by resistance thermometers or thermocouples. The temperature measured is however the temperature of the environment in which the sheets lie, and not the sheet temperature or the temperature of the paint layer to be dried. Moreover, manual temperature setting based on experience does not have the merit of being sufficiently precise or responsive to effective requirements. If on the basis of experience a given temperature profile is used in the oven, it cannot be ensured that the temperatures used are those effectively necessary for implementing the required paint drying or that the paint will assume the temperature necessary for this (in this respect it should be noted that both the glass thickness and the paint thickness and viscosity affect the temperature acquired by the paint at the oven outlet, other conditions being equal).